Referring to FIG. 9, a conventional two-stroke internal combustion engine contains a cylinder 1, a crankcase 2 fixed on a bottom of the cylinder 1, a piston 3 mounted in the cylinder 1, a crankshaft 201 accommodated in the crankcase 2, a connection rod 4 connected between the crankshaft 201 and the piston 3, and a spark plug 5 secured on a top of the cylinder 1. The cylinder 1 includes a combustion chamber 6 defined therein, a gas inlet 7, a gas outlet 8 and a purge orifice 9 which are arranged on a peripheral wall of a body of the cylinder 1. When the internal combustion engine purges gas after exchanging the gas, the crankshaft 201 drives the connection rod 4 to actuate the piston 3 to move downward so as to open the purge orifice 9, hence exhaust gas is pushed from the purge orifice 9 and is discharged out of the gas outlet 8, thus finishing gas purge process.
Because the internal combustion engine purges the gas so as to remove the exhaust gas from the crankcase, it is difficult to arrange the gas inlet 7, the gas outlet 9, and the purge orifice 9 in the cylinder 1. To satisfy the gas purge of the purge orifice 9, the body is winging and is complicated, so it is impossible to cut and machine the cylinder by using a machining center. To overcome above-mentioned problem, the cylinder is sand casted (or gravity casted) by mating with precision dewaxing so as to obtain casting components having above-mentioned structure and to form the purge orifice integrally formed with the body of the cylinder. However, the cylinder is produced slowly at a high fabrication cost.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.